In high frequency oscillators that magnetically insulate the region or a "gap" in which electrons flow from cathode to anode, the magnetic insulation is provided by a magnetic field that is generated from external electromagnets. However, in this type of insulation there is a need to constantly match the voltage applied to the oscillator with the magnetic field supplied by the electromagnets. It would be desirable to provide a microwave oscillator that does not require such voltage matching.
Because magnetically insulated microwave oscillators require two power sources, one to energize the oscillator and another to establish the magnetic insulating field by the external electromagnets; there is a tendency toward electrical breakdown as higher applied voltages are approached. It naturally is desirable to reduce this breakdown tendency as high voltages are approached.
Known microwave oscillators using magnetic insulation tend to have a high inherent impedance. Such devices are used for plasma heating, electromagnetic effects, and RF accelerator applications. This high impedance severely limits the power level at which the oscillators can operate. It accordingly would be desirable to provide a microwave oscillator that has a lower inherent impedance than known oscillators to operate at significantly higher power levels.
There are numerous devices for producing microwaves using slow-wave structures (slow-waves are waves having phase velocity less than the speed of light). Therein an electron beam interacts with fundamental oscillation modes of the device, and the interaction produces microwave energy at the expense of beam energy. However, known microwave oscillators using slow-wave structures employ magnetic fields applied by external magnets to provide magnetic insulation, and have the disadvantages characterized above.
In Bekefi et al, Microwave Emission from Magnetically Insulated Relativistic Electron-Beam Diodes, 1st IEEE International Pulsed Power Conference, 1976, there is a suggestion that self-generated magnetic fields could be self-generated within a cathode of a non-slow-wave magnetically insulated microwave generator.
Microwave generators are generally plagued with the problem of "chirping" when voltage variations are applied thereto (chirping is defined as changes in frequency of the produced microwave energy as a function of changes or variations in voltage applied to the microwave generator). The voltage variations are generally unplanned and difficult to control, and the resulting chirping is an undesirable characteristic that is difficult to prevent.